Disposable surgical safety scalpel

ABSTRACT

A disposable surgical safety scalpel comprising a blade, fixed at one end to an elongated support or slider, sliding longitudinally inside a protective shell, to bring the blade from a retracted inoperative position, in which it is housed inside the shell, to an exposed operative position, through the action of an operator who acts on a push-button mounted on the support; a safety shield longitudinally slidably mounted on the shell, the shield moving from an advanced position, in which it covers the push-button, when the push-button is in its retracted inoperative position, for preventing the push-button from involuntary driving, to a retracted position, in which the shield does not cover the push-button; and elastic return elements to bring the blade back into the retracted inoperative position, the elastic elements acting between the support and the safety shield, such that the shield can automatically and involuntary cover the push-button, when the support is brought in its retracted inoperative position by the elastic elements.

The present invention relates to a disposable surgical safety scalpelfor medical use, having a retractable blade.

A scalpel is a highly professional surgical instrument which has beenperfected over the years to such an extent that it cannot be compared toa jack knife or a cutter.

In describing the prior art, reference can be made only from anhistorical viewpoint to some patents relating to knives described in themore or less recent past, whose characteristic was to have a blade thatis positioned after use in a protective container.

This is the case, for example, of the following patents:

GB- 5487 (LAKE), which as far back as 1884 described a knife with anextractable blade;

U.S. Pat. No. 4,028,758 (O'CONNOR), which describes a combination of autility knife and a staple remover;

U.K.-1511889 (STEABBEN), which describes a pocket cutter with a bladethat retracts but not automatically;

U.S. Pat. No. 4,769,912 (DAVIS), which describes a knife with anacceleration sensor;

U.S. Pat. No. 4,858,320 (LEMAIRE), which describes a pocket knife withretractable blade;

DE-3735294 (TEIHS), U.S. Pat. No. 4,835,865 (KNOOP) and lastlyBE.1.002.554 (VAN HOOYDONCK), which describe an industrial cutter withretractable blade.

As it is well known, the surgical scalpels existing on the market are ofthe disposable or reusable type, with a fixed or interchangeable blade,and do not normally have any protection, except for a blade protectingcap in the case of disposable scalpels, which cap is slipped off beforeuse and could be replaced after use.

In fact the cap should never be replaced because this maneuver can causeunwelcome cuts, with the risk of transmission of diseases, includingserious ones like AIDS and viral hepatitis.

The use of a barrier system, such as gloves with a steel mesh, whichprotect from cuts but not from stab wounds, is not well accepted becauseof the increased thickness and stiffness of the gloves, which leads to aloss of sensitivity.

The use of a different system, called “Magnetic Drape”, which consistsof a sort of magnet cloth to be placed near the operating field and towhich the surgical instruments adhere through the action of a magnet,avoids the stage of passing the instruments from hand to hand, thuseliminating some wounds, i.e. those that occur during exchange ofinstruments between operators.

This system is poorly received by surgeons because it is essential tolook away from the operating field to grasp the instrument and alsobecause it is of no use for non-metallic objects.

The majority of accidental scalpel stab wounds or cuts occurs not somuch when the surgeon makes an incision in the patient's skin or tissueas when the scalpel is passed from hand to hand by the medical operatorsor during disposal.

A study published in the USA in April 1995 by Dr. Janine Jagger in“Advances in exposure prevention”, Volume 1 No. 3 published by“INTERNATIONAL HEALTH CARE WORKER SAFETY RESEARCH AND RESOURCE CENTER”showed that 34% of scalpel wounds occur during use of the instrument,whilst the remaining 39% and 27% , respectively, take place when thescalpel is passed from hand to hand by operators and during removalreplacement-disposal of the blade.

From these data it emerges that, overall, scalpels with an exposed bladeor an interchangeable blade are responsible for 66% of cut wounds thatoccur among medical operators before, during and after use of theinstrument.

It is for this reason that all scalpels with an exposed blade, such asthose currently on the market, must be considered dangerous, as well asthose with an interchangeable blade, such as those forming the object ofthe following patents:

PCT-WO 90/11725 (DOLGIN), which describes a metal scalpel with a mobileguard, with no automatic return and requiring replacement of the blade;

U.S. Pat. No. 5,250,063 (ABIDIN), which describes a metal scalpel with amobile guard and an interchangeable blade;

PCT-WO 94/13216 (WERNER), which describes a metal scalpel with avoluntarily and automatically retracting blade that is extremelydangerous in that, pressure exerted on the rear part causes anaccidental forward movement of the blade, is difficult to construct andalso has an interchangeable blade;

PCT-WO 95/15723 (GHARIBIAN), which describes a scalpel with a mobileguard and interchangeable blade without any locking system between thecap and the blade holder, making it difficult to use and dangerous;

PCT-WO 93/24064 (NEWMAN P. H.) and U.S. Pat. No. 5,403,337 (PLATTS)which describe a disposable scalpel with a blade that can be changedduring the surgical procedure, without foreseeing any protection forused blades.

Changing of the blade is in fact the weak point of any instrument, eventhose considered safe, because handling necessarily leads to anincreased risk of accidental wounds.

In the analysis of the prior art it can be seen that as time went on,inventors refined the idea of a safe scalpel to meet the need forprotection required by surgeons.

Starting from mobile blade protection system without automatic return,such as, for example, those described in patents:

U.S. Pat. No. 3,905,101 (SHEPHERD), U.S. Pat. No. 3,906,626 (RIULI),U.S. Pat. No. 4,414,974 (DOTSON), EP-0 251 485 (GORDY), U.S. Pat. No.4,735,202 (WILLIAMS), EP-0 612 506 (NEWMAN C. D.), whose main defectslie in the need to use both hands to set up or to protect the instrumentand the necessity to remember to cover the blade each time it is passedfrom hand to hand, systems have been designed with a mobile blade guardthat can be moved with only one hand, but still without automatic returnof the cap, such as those described in patents:

PCT-WO 90/11725 (DOLGIN), U.S. Pat. No. 5,250,063 (ABIDIN), U.S. Pat.No. 5,417,704 (WONDERLEY), PCT-WO 95/15723 (GHARIBIAN), in whichadvancement and retraction of the protective cap is carried out with onehand and must be intentional on the part of the operator.

Again with regard to mobile guard, the following patents must beconsidered separately:

U.S. Pat. No. 5,330,492 (HAUGEN), which describes a scalpel with a guardthat can be moved by means of a push-button, which when pressed causesthe protective cap to retract, uncovering the blade, and when releasedunintentionally causes the opposite effect; this instrument must begrasped in a an unnatural way, does not offer guarantees of safetybecause the push-button protrudes excessively and in addition, becauseof its excessive height, does not allow a correct cutting angle on theskin surface;

U.S. Pat. No. 5,330,494 (VAN DER WESTHUIZEN), which describes a guardthat can move transversely to the blade, constituting a danger not onlyfor the operators, because pressure exerted-casually on the lower edgeof the cap causes uncovering of the blade with a high risk of wounds,but also for patients, since the cutting force cannot be regulated.

More recently different systems have been proposed, such as, forexample, that in U.S. Pat. No. 5,116,351 (FRASSETTI), which describes amobile blade mechanism, with automatic return of the blade to theprotected position and with the possibility of voluntary locking, but itis basically awkward, because it obliges the operator to work in anunnatural position, that is with the finger exerting a certain pressureon the upper edge of the blade and with the blade partly covered by theprotection system;

and that of U.S. Pat. No. 5,207,696 (MATWIJCOW), which describes ascalpel with a retractable blade and mobile guard, but which seems toobulky and therefore awkward and has no automatic involuntary return ofthe blade to the covered position.

A further development in the design of these instruments has come aboutwith a concept that foresees the possibility of extracting the bladefrom the handle. This is probably the idea that holds most advantages,because it offers interesting solutions to the problems described up tonow, although each of the ideas proposed gives rise to someconsiderations as regards their practical operation.

A first proposal for a retractable blade is presented in:

EP-0 217 638 (DESATNICK), which describes an instrument for closedcavity surgery, with a small retractable blade, without automaticreturn, not disposable, therefore dangerous during blade changes, andnot suitable for skin incisions;

PCT-WO 93/24064 (NEWMAN P. H.), which describes a scalpel with lockingof the exposed blade, which is very difficult to set up, with voluntaryreturn, with the risk of the blade holder with the blade coming outaccidentally from the rear part of the cover, without any protectionagainst an accidental forward movement of the blade and with thepossibility of replacing the blades during a surgical procedure, anoperation which seems dangerous because the exposed blade is handled;

U.S. Pat. No. 5,330,493 (HAINING) which describes a disposable scalpelwith a retractable blade, without automatic return of the blade to theresting position, with a button for forward movement of the blade thatis situated on its upper edge and is therefore awkward to slide, andwith a permanent end-of-use lock, which seems superfluous and couldsometimes be applied accidentally, thus making it impossible to use theinstrument;

PCT-WO-94/13216 (WERNER), which describes a metal scalpel with voluntaryautomatic retraction of the blade that is extremely dangerous because apressure exerted on its rear part causes an accidental unintentionalforward movement of the blade. Said metal scalpel is difficult toconstruct and furthermore has an interchangeable blade;

U.S. Pat. No. 5,344,424 (ROBERTS) which presents a disposable scalpelwith voluntary retraction, with three locking positions, i.e. anoperative or set up position, an inoperative position and a safetyposition, where the only innovation appears to be the internal safetydevice, but which is difficult to handle and dangerous because the bladeadvance system protrudes too far;

U.S. Pat. No. 5,531,754 (SHACKELFORD), which presents a scalpel withvoluntary retraction, but dangerous because the blade advance systemprotrudes too high;

EP-0 622 047 (DERBYSHIRE), which describes an original blade advancesystem in which pressure is exerted on a flexible container (balloon),with automatic spring-operated return, with the defect that seeing theblade retract each time, pressure is exerted on skin or tissues becauseof the intrinsic elasticity of the balloon itself, and the blade canaccidentally move forward through unintentional pressure exerted byother instruments or hands;

U.S. Pat. No. 5,403,337 (PLATTS), which describes a scalpel whollysimilar to the one described in PCT-WO 93/24064 (EWMAN P. H.),criticizing it as awkward and dangerous and adding its own smallmodification to eliminate these defects, but making it more difficult toset up with only one hand (the rear part of the handle has been widenedto allow for positioning of two stops) and still foreseeing bladechanges during the surgical procedure, which continues to represent ahazard;

U.S. Pat. No. 5,431,672 (COTE), which presents a scalpel with automatic,voluntary return of the blade with an additional internal lock, whichcould be accidentally applied during surgical procedures, forcing themedical staff to use a new scalpel;

PCT-WO-95/24855 (DILLON), which shows a scalpel with automatic,voluntary blade return, with an unsafe stopping system for the exposedblade and with locking devices not better identified to avoid re-use;

PCT-WO 93/25152 (FLUMENE et al.), which presents a disposable scalpelwith rear lock to prevent any accidental forward movement of the blade,with easy blade exposure, without any locking in the operative or set upposition of the blade, so as to have automatic, involuntary return andlocking in the resting position; moreover, a particular characteristicis the possibility of graduating extraction of the blade according tothe type of incision, always acting on the instrument in a comfortable,ergonomic position; the only drawback to be noted is that since it doesnot have a forward lock, use of this instrument is rather awkward insome operating conditions, so the presence of a stop device for theblade in operative position could be desirable in some circunstances;

U.S. Pat. No. 6,022,364 (FLUMENE et al.), which describes a disposablescalpel with the same features of PTC-WO 93/25152, but with a blade'svoluntary lock in position of use, which the operator can operate ornot, depending on how he prefers to work. The scalpel has a furtherlock-safety-cover system, which operates at the end of a retractionstroke of the blade, thus avoiding an accidental emerging of the same.

The aim of this invention is, therefore, to solve some of the drawbacksposed by the prior art.

In particular, an aim of the invention is to provide a scalpel that issafe when passed among the operators, protected during transport anddisposal of used materials, and to offer different possibilities of use,so that it is accepted by virtually all users, irrespective of theirpreferences for handling of the instrument.

Another aim of the invention is to provide safety locks for the bladethat can easily be removed by moving one finger of the hand holding thescalpel, which is the same finger used to advance the blade.

Yet another aim of the invention is to provide a safety scalpel of theabove type that is easy to make, automatically assemblable andeconomical.

A surgical safety scalpel in accordance with the invention ischaracterized by the characteristics listed in appended independentclaim 1.

Essentially, the scalpel according to the invention is provided with avoluntary locking means for intentionally locking the blade in positionfor use, which the operator can operate or not, depending on how heprefers to work.

If this locking means is operated, it must be disabled after use toallow return of the blade.

However, this maneuver is extremely simple and does not requireparticular care on the part of the user.

An essential feature of the present invention lies in the presence of anautomatic safety-cover system of the push-button of the blade, whichautomatically operates at the end of a retraction stroke of the blade,thus avoiding an unintentional driving of the push-button and thereforean accidental emerging of the blade.

An advantage of the present invention lies in the fact that themaneuvers made on the scalpel (retracting the push-buttoncover—advancing the blade—inserting and releasing the front lock of theblade when required) are effected by means of a single finger of a samehand, keeping the scalpel in its correct use position and leaving theother hand free to make another action.

Further characteristics of the invention will be made clearer by thefollowing detailed description, referring to purely exemplary andtherefore non-limiting embodiments thereof, illustrated in the appendeddrawings, in which:

FIG, 1 is a top plan view of a scalpel according to the invention, withthe blade retracted inside the shell, in an inoperative position;

FIG. 2 is a median sectional view, taken along the line 11—11 in FIG. 1;

FIG. 3 is a median sectional view, taken along the line II—II in FIG. 1,showing the push-button safety cover member in a retracted position;

FIG. 4 is a top plan view of the scalpel in FIG. 1, with the bladeextracted, in the operating position;

FIG. 5 is a median sectional view taken along the line V—V in FIG. 4,showing the blade extracted, in the operating position, not locked withthe voluntary lock;

FIG. 6 is a median sectional view taken along the line V—V in FIG. 4,showing the blade extracted, in the operating position, locked with thevoluntary lock;

FIG. 7 is a top plan view of the safety handle of the scalpel;

FIGS. 7A, 7B, 7C are cross-sections taken along the planes A—A, B—B andC—C, respectively, in FIG. 7;

FIG. 8 is a plan view of the rear plug of the safety handle;

FIG. 9 is a top plan view of the sliding blade support, to be assembledinside the safety handle;

FIG. 10 is a lateral view of safety cover member of the bladepush-button;

FIG. 11 is a lateral view of the sliding blade support, that must beassembled and fitted inside the safety handle;

FIG. 12 is a top plan view of a second embodiment of the rear plug;

FIG. 13 is a lateral view of the second embodiment of the rear plug inan unlocked position;

FIG. 12A is a median sectional view, taken along the line A—A in FIG.12, showing the rear plug in an unlocked position;

FIG. 14 is a lateral view of the second embodiment of the rear plug in alocked position;

FIG. 12B is a median sectional view, taken along the line A—A in FIG.12, showing the rear plug in a locked position;

FIG. 15 is a top plan view of the scalpel with the second embodiment ofthe rear plug;

FIG. 16 is a median sectional view, as FIG. 2, showing the scalpel withthe second embodiment of the rear plug in an unlocked position;

FIG. 17 is a median sectional view, as FIG. 2, showing the scalpel withthe second embodiment of the rear plug in a locked position.

With reference to the appended drawings, and for now to FIGS. 1-6 inparticular, a safety scalpel, according to the invention, has beendesigned as a whole with reference numeral 1.

It comprises a scalpel proper 2, consisting of a blade 3 and anelongated support 4, and a shell or outer case 5, acting as a handle,made in two members: the shell proper 5 and a rear closure or plug 7,joined together by mortising.

The scalpel 2 is housed inside the shell 5, which has two ends, ananterior open end 9 and the opposite end closed by the plug 7, and hasthe possibility of sliding longitudinally, in such a way that the blade3 can be brought from a resting or inoperative position in which it ishoused completely inside the shell 5 (FIGS. 1, 2 and 3), to an operativeposition or position for use, in which it projects from the open end 9of the shell 5 (FIGS. 4, 5 and 6).

The elongated support 4 of the blade 3 acts as a slider and is guidedbetween the side walls of the shell 5. Referring to FIG. 7 on one ofthese side walls, a longitudinal aperture or window 6 is provided, witha substantially rectangular shape, with a narrowing 26 at the front, onthe part wherein the blade 3 is positioned. The front narrowing 26creates an abutment surface 27 in the window 6.

A push-button or pivoted button 13 of the support 4 is provided in thewindow 6, protruding only slightly from the window 6, the operator beingable to operate said button with one finger to cause the support-slider4 to slide. To make the button 13 easier to grip, normally with thethumb, herring-bone ribs 14 are provided on it.

The support 4 is held in its retracted position when it is housed insidethe shell 5 by an elastic means, in particular by a compression spring15 operating between a small pin 16 projecting downward from a safetycover 18 (hereinafter called shield) of push-button 13 and the rear wall25 of a cavity 10 for housing the spring 15, located in the rear part ofthe support 4 of the scalpel proper 2.

The oscillating button 13 pivots on a pin 12, disposed transversely tothe support 4.

The push-button 13 is so shaped that its rear part 21 (with reference tothe appended figures), has a lower height than the height of the frontpart 20, to easier the grip of the user.

A circular open housing 22, provided below the push-button 13, in thefront part thereof, engages a transversal pin 23 provided in an opening24 of the handle 5, when the user voluntarily operates the button 13,thus providing a voluntary lock for the blade in condition of use.

FIGS. 1-6 and 10 also show the safety shield 18 covering the push-button13, that is the shield 18 is able to prevent the push-button 13 fromaccidentally driving and to prevent therefore the blade from emerging,when the scalpel is passed from hand to hand. The shield 18 slideslongitudinally into the side walls of the window 6 between the support 4and the shell 5.

The safety shield 18 comprises a safety cover 17, C-shaped in crosssection, on the front part thereof, covering the push-button 13 (seeFIGS. 1 and 2), preventing any pressure on the push-button itself; and alug 19 on the rear part thereof, covering the spring 15 housed in thecavity 10.

The pin 16, projecting from the lower part of the shield 18, pushes thespring 15 to the rear wall 25 of the cavity 10. Therefore, the shield 18can slide from an advanced position, wherein its front end is inabutment against the abutment surface 27 of the narrowing 26 of thewindow 6 of the shell 5 to a retracted position, wherein the spring 15is compressed between the pin 16 and the wall 25 of the support 4. Whenthe shield is in the advanced position, it covers the push-button 13;when it is in retracted position, the push-button 13 is uncovered.

FIGS. 12-17 show a second embodiment of the rear plug 7, which isdesigned as a whole with reference numeral 107.

The rear plug 107 comprises an oscillating push-button 109, that pivotson two aligned pins 108, fitted transversely to a frame of the rear plug107. The oscillating push-button 109 comprises a rear part 112 with apin 113 protruding downward therefrom. The pin 113 comprises tworadially protruding collars, delimiting a first and a second annularnotch 114, 115, respectively.

A through hole 8 is provided in the rear part of the shell 5, bettershown in FIG. 8. When the rear plug 107 is assembled in the rear part ofthe shell 5, the pin 113 engages the hole 8, and precisely the firstnotch 114 of the pin 113 is engaged into the hole 8. In this condition,(FIG. 16), the front end 110 of the oscillating push-button 109 is atthe same level of the frame of the rear plug 107 and the scalpel is inoperative condition.

The working position of the button 109 (as shown in FIG. 16) allows thesliding movement of the shield 18, since the rear end of the shield 18does not interfere with oscillating push-button 109.

At the end of the surgical operation, before the disposal of thescalpel, the user has merely to press the rear part 112 of theoscillating push-button 119 of the rear plug 107; thus the pin 113,housed in the hole 8 with the first notch 114, penetrates in the hole 8more deeply up to the second notch 115. After this movement, the frontpart 110 of the push-button 109 protrudes upwardly from the frame of therear plug 107 and it is opposed to the rear part 19 of the shield 18 andtherefore the scalpel cannot be used again.

The scalpel according.to the invention works as follows.

When the scalpel is not in use, the spring 15 holds the scalpel 2 in aretracted position inside the shell 5, as shown in FIGS. 1 and 2, by acombined action of the spring 15, the scalpel 2 and the shield 18. Oneof the two contact points of the spring 15 is the pin 16 of the shield18, and the other contact point is the rear wall 25 of the cavity 10 ofthe scalpel proper 2.

The scalpel proper 2 is housed inside the shell 5, longitudinallysliding therein. The rear cover 7 or 107 prevents the scalpel proper 2from exiting from the rear end of the shell 5.

Only the scalpel blade 3 can emerge from the front opening 9 of theshell 5. The scalpel proper 2 is prevented from extraction from thefront end of the shell 5 because the front end of the push-button 13abuts against the front end of the restriction 26 of the window 6 of theshell 5.

Starting from the position shown in FIGS. 1 and 2, in order to use thescalpel, it is first necessary to move the safety shield 18 backwards,with the thumb of one hand, as shown in FIG. 3. It is thereforesufficient to exert a light pressure on the pivoted push-button 13, withthe same thumb, and push the button 13 forwards, in the direction of theopen end 9 of the shell 5, so as to cause the blade 3 to emerge, asshown in FIGS. 4 and 5.

In this condition, the scalpel is ready for use, without the blade beinglocked in this position, said locking takes place only through avoluntary action on the part of the surgeon, as it will be seen withreference to FIG. 6.

Remaining within the context of FIGS. 4 and 5, after use of theinstrument, simply releasing the push-button 13 causes the blade toreturn automatically inside the shell 5, through the action of thespring 15, with consequent automatic and involuntary covering of thepush-button 13 by the shield 18.

The use of the scalpel shown in FIGS. 4 and 5, without locking of theblade, is suitable for that group of users that prefers automatic andinvoluntary return of the blade 3 after use, without any maneuver havingto be carried out.

An alternative use of the scalpel according to the invention is shown inFIG. 6, in which locking of the blade 3 has taken place, through avoluntary action by the user, by means of engagement of the housing 22of the button 13 with the pin 23 provided in the shell 5.

After use of the scalpel, pressure must be exerted on the rear part 21of the pivoted push-button 13, to cause the disengagement of the housing22 of the push-button from the pin 23 of the shell 5 and therefore theunlocking of the blade and its automatic and voluntary return inside theshell 5.

The shell 5, the support 4 and the pivoted push-button 13 areadvantageously made of plastic, whilst the spring 15 can be of plastic,metal, rubber or with an air or gas system or the like.

It is also obvious that the blade 3 can have any shape, depending on itsuse, without the characteristics of the scalpel according to theinvention undergoing any changes.

To aid voluntary locking of the blade in the position for use (FIG. 6),the horizontally pivoting push-button 13 has the raised part 20 at thefront, which facilitates the lowering action to cause engagement of itshousing 22 with the pin 23.

According to the embodiment shown in FIGS. 12-17, at the end of theoperation it is possible to put the scalpel in a safe condition,pressing the rear part 112 of the button 109, housed in the rear plug107. This position definitively locks the shield 18, making the scalpelnot reusable and no longer dangerous.

What is claimed is:
 1. A disposable surgical safety scalpel comprising:a blade (3), fixed at one end to an elongated support or slider (4),sliding longitudinally inside a protective shell (5), to bring saidblade (3) from a retracted inoperative position, in which it is housedinside the shell (5), to an exposed operative position, through theaction of an operator who acts on a push-button (13) mounted on saidsupport (4); a safety shield (18) longitudinally slidably mounted onsaid shell (5), said shield (18) moving from an advanced position, inwhich it covers said push-button (13), when said push-button is in itsretracted inoperative position, for preventing the push-button frominvoluntary driving, to a retracted position, in which said shield doesnot cover said push-button; and elastic return means (15) to bring theblade (3) back into the retracted inoperative position, characterized inthat said elastic return means (15) act between said support (4) of theblade (3) and said safety shield (18), so that said shield (18) canautomatically and involuntary cover the push-button (13), when saidsupport (4) is brought in its retracted inoperative position by saidelastic means.
 2. The scalpel according to claim 1, characterized inthat a cavity (10) is provided in the rear part of said support (4),said cavity (10) being able to house said elastic return means (15),which act between a pin (16) protruding downwardly from said shield (18)and a rear end wall (25) of said cavity (10) of said support (4).
 3. Thescalpel according to claim 1, characterized in that said shield (18)comprises a front part (17) having a substantial C shape incross-section, able to cover said push-button (13) and a substantialflat rear part (19) located onto said shell (5).
 4. The scalpelaccording to claim 1, characterized in that said support (4) is housedinto the shell (5) between the side walls of the shell and is covered bythe shield (18), so that said shield (18) and said support (4) can slideon parallel surfaces, and said elastic means (15) can guarantee both thereturn of said support (4) in the shell (5) and the positioning of saidshield (18) in said advanced position covering the push-button (13). 5.The scalpel according to claim 1, characterized in that said shell (5)comprises a front stop member (27) to stop the forward stroke of sideshield (18) and a rear stop member (7, 107) to stop the reverse strokeof said support (4) and/or said shield (18).
 6. The scalpel according toclaim 5, characterized in that said front stop member is an abutmentsurface (27) of a narrowing (26) of a window (6) of said shell (5) whichallows sliding of said push-button (13) and said shield (18), and saidrear stop member is a rear plug (7; 107) able to be fitted in the rearpart of said shell (5).
 7. The scalpel according to claim 6,characterized in that said rear plug (107) comprises locking means (109)to lock/unlock said shield (18).
 8. The scalpel according to claim 7,characterized in that said locking means is an oscillating push-button(109) having a front part (116) able to abut against the rear end of theshield (18) to lock it and a rear part having a pin (113) protrudingdownwardly therefrom to engage into a hole (8) provided in said shell(5).
 9. The scalpel according to claim 8, characterized in that said pin(113) has two collars delimiting a first notch (114) and a second notch(115) which define with said hole (8) a first engaging position, inwhich the push-button (109) does not lock the shield (18) and a secondengaging position, in which the push-button (109) locks the shield (18).10. The scalpel according to claim 1, characterized in that saidpush-button (13) is pivotly mounted on said support (4) and providesengaging means (22) engageable with respective engaging means (23)provided in said shell (5) by means of voluntary pression on saidpush-button (13) by the user, when the blade is in said exposedposition.
 11. The scalpel according to claim 2, characterized in thatsaid shield (18) comprises a front part (17) having a substantial Cshape in cross-section, able to cover said push-button (13) and asubstantial flat rear part (19) located onto said shell (5).